1. Field of the Invention
The present invention relates to light emitting nitride semiconductor devices employing a nitride compound semiconductor (InxAlyGa1-x-yN, where 0≦X, 0≦Y, and X+Y<1).
2. Description of the Background Art
A conventional light emitting nitride semiconductor device's structure described in Japanese Patent Laying-Open No. 08-274372 is shown in FIG. 11. In the figure the conventional light emitting device has a sapphire substrate 101 and thereon a buffer layer 102 of Al0.1Ga0.83In0.07N of 500 Å is deposited. On buffer layer 102 an n+ layer 103 is formed of silicon doped GaN and having a thickness of approximately 2.0 μm and an electron density of 2×1018/cm3. On n+ layer 103 excluding a portion provided with an electrode 201 are sequentially deposited an n+ layer 104 of high carrier concentration formed of silicon doped (Alx2Ga1-x2)y2In1-y2N and having a thickness of approximately 2.0 μm and an electron density of 2×1018/cm3, a light emitting layer 105 of p conductivity formed of magnesium (Mg), cadmium (Cd) and silicon doped (Alx1Ga1-x1)y1In1-y1N and having a thickness of approximately 0.5 μm, a p+ layer 106 formed of Mg doped (Alx2Ga1-x2)y2In1-y2N having a Mg content of 1×1020/cm3 and a hole density of 5×1017/cm3, and having a thickness of approximately 1.0 μm, a second contact layer 107 formed of Mg doped GaN having a Mg content of 1×1020/cm3 and a hole density of 5×1017/cm3, and having a thickness of approximately 0.2 μm, and a first contact layer 108 formed of Mg doped GaN having a Mg content of 2×1020/cm3 and a hole density of 2×1017/cm3, and having a thickness of approximately 500 Å.
Furthermore there are also deposited an electrode 202 connecting to the first contact layer 108 and electrode 201 connecting to n+ layer 103 on an exposed surface. Electrode 202 includes on the first contact layer 108 a layer 109 of titanium (Ti) deposited to have a uniform thickness of 20 Å and a layer 110 of nickel (Ni) deposited to have a thickness of 60 Å. These two layers function as a transparent electrode. Layer 110 has a portion having deposited thereon a layer 111 of Ni having a thickness of 1,000 Å and functioning as a pad having a wire bonded thereto and a layer 112 of gold (Au) having a thickness of 1.5 μm. Electrode 201 has a 3-layer structure formed of a layer 113 of aluminum (Al) having a thickness of 500 Å and bonded on n+ layer 103, a layer 114 of Ti having a thickness of 5,000 Å and a layer 115 of Au having a thickness of 1.5 μm.
In such a light emitting nitride semiconductor device's structure an LED has an upper surface with layer 109 of Ti and 20 Å in thickness and layer 110 of Ni and 60 Å in thickness deposited in two layers to serve as a transparent electrode. These thin metal films, however, provide poor reflectance and transmittance and absorb a large quantity of light, resulting in poor optical extraction efficiency.
As another example, Japanese Patent Laying-Open No. 11-168235 describes a light emitting nitride semiconductor device having a structure as shown in FIG. 12. With reference to the figure, on a substrate 121 an interconnect pattern 122 is provided and thereon via a bump 125 an LED chip 123 is mounted. LED chip 123 has a bottom surface provided with a reflection layer 124, and thereunder underfill resin 126 is introduced.
The light emitting nitride semiconductor device thus structured provides improved optical extraction efficiency by reflecting light by reflection layer 124 to extract the light at a surface which is not provided with an electrode of LED chip 123. However, as chip 123 and layer 124 are mounted on the substrate via bump 125, it is difficult to align interconnect pattern 122 and bump 125, resulting in poor yield.
The present invention has been made to overcome the above described conventional technological disadvantage and it contemplates a light emitting nitride semiconductor device that allows light generated by the device to be extracted more efficiently and also provides satisfactory yield, and a method of fabricating the same.